Modern internal combustion engines with compression ignition are commonly controlled such that a portion of exhaust gas is mixed with clean intake air to improve emissions performance. This technique is known as In Cylinder Charge Dilution (ICCD). Using ICCD, i.e., introducing exhaust gas back into the combustion chamber, has a particularly positive influence on the emission levels of various nitrogen oxides, commonly referred to as NOx. However, the introduction of exhaust gas tends to have a negative influence on the level of particulate matter (PM) resulting from the combustion. This balance between NOx and PM, in relation to the introduction of certain levels of exhaust gas, is known as the PM-NOx trade-off. Both PM and NOx emissions are the subject of stringent regulations. Controlling the amount of exhaust gas transferred back into the combustion chamber is a significant factor in ensuring that both PM and NOx levels are within regulation limits. It would therefore be beneficial to exert control over the amount of exhaust gas transferred into the combustion chamber.
One known method of providing exhaust gas to the combustion chamber is by opening an exhaust valve during an intake stroke of the piston so that previously expelled exhaust gas is transferred back from the exhaust manifold into the combustion chamber. Various mechanical arrangements are known to enable opening of the exhaust valve and to be able to vary the intake of exhaust gas to a certain extent. A common solution is to provide an additional cam surface on a camshaft so as to open the exhaust valve.
However, such arrangements are inflexible in that it is not possible to select a mode in which no exhaust gas is taken back into the combustion chamber, a mode which may be desirable during transient states of the engine. In addition, it is not possible to influence the amount of exhaust gas taken back in.
The present disclosure is directed to one or more improvements in the existing technology.